WordPress: Select post parent from another post type

gistfile1.txt

add_action('admin_menu', function() {
	remove_meta_box('pageparentdiv', 'chapter', 'normal');
});
add_action('add_meta_boxes', function() {
	add_meta_box('chapter-parent', 'Part', 'chapter_attributes_meta_box', 'chapter', 'side', 'high');
});

function chapter_attributes_meta_box($post) {
	$post_type_object = get_post_type_object($post->post_type);
	if ( $post_type_object->hierarchical ) {
		$pages = wp_dropdown_pages(array('post_type' => 'part', 'selected' => $post->post_parent, 'name' => 'parent_id', 'show_option_none' => __('(no parent)'), 'sort_column'=> 'menu_order, post_title', 'echo' => 0));
		if ( ! empty($pages) ) {
			echo $pages;
		} // end empty pages check
	} // end hierarchical check.
}

Original from http://janina.tumblr.com/post/3588081423/post-parent-different-type